I don't understand how the Mac Studio isn't the redesigned Mac Mini Pro.
Gurman said the "Apple Silicon" Mac Pro was "half the size" of the current Mac Pro. The Studio is no where near half the size. Closer to a 1/4 the size (volume) than to 1/2 the size ( technically down in the 10% range).
There were very good chance the "half sized" Mac Pro was going to have PCI-e slots. Perhaps not 400W video card sized slots but at least a few for storage , A/V capture , networking, etc.
"half sized" means that some of the slots ( and drive mount frame points) were going to disappear but it would be substantially bigger than a Mini or a 3x Mini stack.
The next Mac Pro probably won't be as highly modular as the current Mac Pro , but it really can't do back to about less than the Mac Pro 2013 levels. Apple basically admitted that had issues on internal storage capacity and scale ( leaning on Thunderbolt too much) and variety of compact high I/O bandwidth integrations.
The Studio does go after the lower end and higher volume of the Mac Pro space though. As Apple outlined, they cover the most popular CPU (12 cores ) and the most frequently bought( from them) GPU moudle W5700 with the Studio. There is a decent set of classic Mac Pro users the Studio covers , but it wasn't some of the more vocal and specialized sets. Apple still probably isn't going to cover "everybody" in the old school Mac Pro group. Lots will camp out in 'protest' on their MP 2019 systems. Apple probably won't care much for several years since those folks will have paid a ton of money to sit out there on the fringe.
There is decent chance Apple punted on a "M1" generation solution because it is probably is somewhat fixed on just the graphics and if going to to be fixed in time 'M2' would be better than the alternative at this point. End of 2022 the kicking sand in the face of W5700 is beating up on a multiple year old GPU. ( If they are waiting on TSMC N3 for the 'large' dies than more manageable package sizes also. They can pull back the size of the dies packaging together. ).
The Studio was/is a bigger 'threat' to a "iMac Pro" (with almost the same LCD screen ) than it is to the top 'half' of the Mac Pro line up. That is why Apple used it to 'transition' the iMac 27" to Apple Silicon. Even Apple presented this as the iMac replacement; not the Mac Pro replacement. ( Yes, it is not a direct replacement for either. Apple is likely going to wait and see about a 'big screen' iMac replacement though. How they are going to position against the Studio is a much thornier problem if there is nothing 'magical' price wise with the screen. There are more than several decent options to pair a Studio with from other vendors. )